Project Summary/Abstract Blindness disables millions of people across the world. In most cases, incurable blindness is caused by damage or dysfunction of the eye, retina, or optic nerve, but the visual cortex is undamaged and potentially functional. There has long been interest in developing a prosthetic device that employs direct activation of the intact visual cortex to restore vision to the blind. Electrical stimulation of a single site in visual cortex (even in blind patients) produces a percept of a distinct spot of light known as a phosphene. It has been speculated that phosphenes could serve as the building blocks for visual restoration in the blind, but it is unknown if individual phosphenes can be treated as virtual pixels and combined to produce perception of complex images. Addressing this issue is critical to determining if direct activation of visual cortex is a viable strategy for restoring useful vision. We propose to study perceptual correlates of visual cortex stimulation in human patients with implanted intracranial electrodes. A major advantage of studying stimulation-induced percepts in humans is that only human subjects can directly report on their perceptual experiences. In Aim 1, we will compare the spatial location and orientation of phosphenes created by artificially stimulating a population of visual neurons with the responses of these same neurons to real visual stimuli. In Aim 2, we will determine if these phosphenes can be used as building blocks for more complex visual percepts (much like pixels in a computer display) a key step towards the long-term goal of developing a cortical visual prosthetic.